Evaluation of the effects of ultra-violet light treatment on quagga mussel settlement and veliger survival at Davis Dam

Dreissenid mussels are aggressive biofoulers that threaten water delivery and hydropower reliability. The use of medium pressure UV systems to control dreissenid mussel settlement in industrial cooling water systems is a desirable alternative to chemical treatments. This paper summarizes two experiments, carried out over two years, using a proprietary medium pressure UV system. The first experiment tested veliger settlement after exposure to doses of 50, 40 and 20 mJ/cm(2). The second experiment tested settlement after exposure to 100 mJ/cm(2), and examined veligers behavior and direct mortality post exposure to UV doses of 100, 50, 40 and 20 mJ/cm(2). All doses tested in the first experiment resulted in settlement reduction between 88 and 99%. The 100 mJ/cm(2) dose reduced settlement by 99%. In the second experiment delayed veliger mortality was observed after every UV level tested. Mortality varied based on UV dose, ambient water temperature, and veliger size.